(1) Field of the Invention
This invention relates to an imaging process and element. The invention relies upon the photoactivated decomposition of a cobalt complex to form products which are especially useful in the initiation of imagewise dye formation. In a preferred form the invention relates particularly to an element having an internal amplification factor.
(2) State of the Prior Art
Non-silver imaging systems of many kinds have been developed in an effort to avoid the increasing cost of silver. However, most of these systems have a speed that is far lower than that achieved by silver. Diazo systems wherein ammonia initiates coupling between a color coupler and unexposed diazonium salt is an example of such a slower, non-silver system.
Another example of a system having a relatively slow speed is one incorporating a salt of a metal ion which is above hydrogen in the electromotive series and, as a photosensitizer, a 9,10-phenanthrenequinone. U.S. Pat. No. 3,561,969 is representative of such a system.
Recently, several non-silver systems based upon the decomposition of cobalt complexes were developed which did have a high gain and therefore increased speed. Commonly owned U.S. application Ser. No. 461,057, entitled "Transition Metal Photoreduction Systems and Processes", filed 15, 1974, by A. Adin and J. C. Fleming, now abandoned in favor of a continuation-in-part application Ser. No. 618,186, filed on Sept. 30, 1975, and now abandoned, discloses phthalaldehyde as a reducing agent precursor. In the last-named application, a leuco dye is added in solution to an already exposed imaging element and undergoes a redox reaction with unexposed inert cobalt (III) complex without requiring the presence of ammonia. The leuco dye, such as leuco malachite green, is not blocked.
An amplification system is disclosed in commonly assigned U.S. application Ser. No. 461,172, filed Apr. 15, 1974, by T. DoMinh, entitled "High Gain Transition Metal Complex Imaging", now abandoned in favor of a continuation-in-part application Ser. No. 627,417, filed on Oct. 30, 1975. The amplification in that case was achieved by incorporating in the element compounds capable of forming at least bidentate chelates with cobalt (II), which act as a catalyst for the reduction of remaining cobalt (III) complexes, thus amplifying the image. However, in such a system care must be taken to exclude acid anions having pKa values high enough to deprotonate the cobalt (II) chelates.
Imaging systems have been developed which rely upon the oxidation of leuco dyes or upon the unblocking of a blocked color coupler or dye to form an image. Representative examples can be found in U.S. Pat. No. 3,615,565, British Pat. No. 975,457 and Research Disclosure, vol. 126, Oct. 1974, Publication No. 12617, Para. III(E)2). These do not however achieve amplification by reason of the oxidation or the unblocking mechanisms.
Oxichromic compounds having a moiety in the form of (COUP)-NH-Ar-X are disclosed in U.S. Pat. Nos. 3,880,658 and 3,935,263, wherein (COUP) is a photographic color-forming coupler and X is a defined moiety, preferably a hydroxyl group. These compounds are not used with cobalt complex chemistry, but rather are directed to silver halide imaging.
Other background references which relate only generally to the field of metallic complexes of amines for imaging include U.S. Pat. Nos. 3,469,984and 2,774,669, and an article by J. Endicott and M. Hoffman in J. American Chem. Soc., Vol. 87, p. 3348, (1965).